Fix ogc/filter

This only compiles if there is goog.provide('ol.Extent') in the typedefs file, and goog.require('ol.Extent') in this file. An alternative is to add an assert statement, but this means an extra dependency.

With this change there is no longer a need for the change to tasks/build.js

src/ol/format/ogc/filter.js

@@ -18,6 +18,7 @@ goog.provide('ol.format.ogc.filter.IsNull');
 goog.provide('ol.format.ogc.filter.IsBetween');
 goog.provide('ol.format.ogc.filter.IsLike');
 
+goog.require('ol.Extent');
 goog.require('ol.Object');
 
 

src/ol/typedefs.js

@@ -2,6 +2,7 @@
  * File for all top-level (in the `ol` namespace) typedefs used by the compiler,
  * and referenced by JSDoc.
  */
+goog.provide('ol.Extent');
 
 
 /**